Sahih Muslim #2639 · The Book of Fasting

Sahih Muslim
Sahih Muslim · Book 13 · The Book of Fasting
Sahih Muslim · كتاب 13 · كتاب الصيام
'A'isha (Allah be pleased with her) reported. In the pre-Islamic days fast was observed on the day of Ashura, but with the advent of Islam (its position was ascertained as that of a voluntary fast). Then he who wished to fast fasted, and he who liked to abandon it abandoned it.
حَدَّثَنِي عَمْرٌو النَّاقِدُ، حَدَّثَنَا سُفْيَانُ، عَنِ الزُّهْرِيِّ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ، - رضى الله
عنها - أَنَّ يَوْمَ، عَاشُورَاءَ كَانَ يُصَامُ فِي الْجَاهِلِيَّةِ فَلَمَّا جَاءَ الإِسْلاَمُ مَنْ شَاءَ صَامَهُ وَمَنْ شَاءَ تَرَكَهُ ‏.‏
Reference : Sahih Muslim 2639In-book reference : Book 13, Hadith 145